Our last two-term leader, George W. Bush, ended his tenure with a financial crash so disastrous that his own party has tried to erase him from memory. Bush's predecessor, Bill Clinton, was more successful, but he still spent much of his second term enmeshed in a sex scandal and battling impeachment.

The soaring ideas and idealism that brought a president victory the first time yield to narrower, more experienced calculations of what he can achieve in practice the second time around. The aides who helped him succeed move on to other jobs, and their successors in the second term often look like the B-team.

A second-term president is a lame duck from election day on; if Congress didn't fear him much before, it will soon fear him even less. And if there's any scandal lurking in an administration's closets, the second term is often when it tumbles into view. Richard M. Nixon's Watergate is the most famous case, but it was only one of many: Reagan had Iran-Contra; Clinton had Monica Lewinsky.

Can Barack Obama escape this iron rule of history? Perhaps — but only if he finds a way to turn his own weakness into an asset.

On the surface, the political foundation of Obama's second term looks weaker than those of his predecessors. All the others — Roosevelt, Eisenhower, Nixon, Reagan, Clinton and Bush — won more votes running for reelection than they had the first time. They succeeded in enlarging their coalitions, not shrinking them. Some won their second terms with landslide margins: Nixon and Roosevelt with 61% of the popular vote.

Obama doesn't have that kind of overwhelming mandate. In 2008, Obama won 28 states and 53% of the popular vote. This year, once the dust settles, he appears likely to win 26 states, with a near tie in the popular vote.

The electorate might well have fired him — except it never warmed to his opponent.

The kind of campaign Obama waged didn't build much of a mandate either. His campaign slogan was almost content-free: "Forward." Much of his pitch was negative, a promise not to enact the conservative changes his opponent was proposing. "We know what change looks like, and what he's selling ain't it," Obama said in his combative stump speeches.

His positive agenda — and he did have one, contrary to what some critics say — was mostly a plea for a chance to "finish the job," to complete the unfinished work of the first term. But as a program for his second term, it's markedly less ambitious than the expansive goals he listed four years ago.

In his most serious policy discussion of the last month — his interview with the Des Moines Register — Obama said his top priorities would be economic growth, deficit reduction and investment in infrastructure, education and energy technology. Those goals are both less ambitious and less specific than the ones set out in his first term, and liberals are likely to see them as a retreat. But with a hostile House of Representatives, it's not at all clear that the president will be able to make much progress even with a more modest set of goals.

Like Mitt Romney, Obama had little choice but to turn toward the center in the final weeks of the presidential campaign. No matter how strong his base of Democratic voters, Obama needed compromise-loving independents to stick with him too.

And Obama has spent plenty of time in the last few weeks talking with Clinton, a supremely pragmatic president who regularly enraged his party's liberal base whenever he thought a lunge to the right might help him pass legislation through a Republican-held Congress.

"I may be the only person in America, but I am far more enthusiastic about President Obama this time than I was four years ago," Clinton said as he campaigned for the president last week.

Why? "He has the right philosophy," Clinton said: "Cooperation works better than conflict. Practical problem-solving is better than ideological extremism."

Two factors will determine what kind of second term Obama has: One is what lessons Republicans draw from their stinging defeat; the other is what lessons Obama takes from the narrowness of his victory.

If we're lucky, we will find that we elected a different Obama from the one who won the presidency four years ago — not just a grayer Obama but a wiser one too.